Electric-discharge device



D. F. RILEY ETAL ELECTRIC-DISCHARGE DEVICE Filed July 23, 1958 Aug. 9,1960 2,948,825 Erasmo-DISCHARGE DEVICE Daniel F. Riley, Braintree,lSeymour Goldberg, Lexington, and Kenneth J. Germeshausen, NewtonCentre, Mass., assignors to Edgerton, Germeshausen and Grier, Inc.,Boston, Mass., a corporation of Massachusetts Filed July 23, 1958, Ser.No. 750,488

`4 Claims. :(Cl. 313-193) The present invention relates to4electric-discharge devices and, more particularly, to gaseous-dischargedevices of the thyratron or rectifier type, and the like.

Electric-discharge devices, of the above-mentioned character, arefrequently used in pulsing circuits, such as, for example, pulsemodulators and the like of the type described in United States LettersPatent Nos. 2,518,879, issued August 15, 1950, and 2,722,629, lissuedNovember l, 1955, to the applicant, Kenneth l. Germeshausen, herein. Oneof the ,problems Vinherent in such use, is that of so-called inversevoltage effects; wherein, 'after `a pulse of current `has been producedin the discharge device, it is desired that the device promptlyY ceaseconducting Vand .remain insensitive to breakdown in `response toVinversely applied voltages resulting from oscillations in the pulsingcircuit, or otherrcause. Particular rceramic envelope discharge tubesthat may lbe subject `to `such diiculty are described, for example, inapplication, Serial No. 599,728, now Patent No.2 j84'2'6'99 filed by.two of the applicants herein, Seymour Goldberg and the said Kenneth L.Germeshausem on July 24 ,1.956, for Gaseous Seal and Method. Y

An object of the lpresent invention, accordingly, is to providea new andimproved electric-discharge device that shall not ybe subject to theVabeve-.rne'nti'oned difficulties and thatshall, to the contrary,be=enabled to hold off fa'r greater inverse voltage 'effect-s than:hasfhereto'farejbeen feasible.

A further object is to provide a new and improved gaseous-dischargedevice of more general character.

`Other and further objects will be explained hereinafter -and will bemore particularly pointed out in the appended claims. In summary, theinvention, from perhaps its broadest point of View, resides in theprovision of an electric-discharge device having a pair of cooperativeelectrodes defining a discharge region therebetween, and disposed in aninsulating envelope, but spaced from the inner wall of the envelope. Aconductive path is disposed external to the discharge region in thespace between the said inner wall and the electrodes, preferably alongthe inner wall. Preferred details are hereinafter set forth.

The invention will now be described in connection with the accompanyingdrawing,

Fig. 1 of which is a longitudinal section of a discharge tube embodyingthe invention in preferred form; and

Fig. 2 is a fragmentary perspective taken along the line 2-2 of Fig. l,looking in the direction of the arrows and showing details ofconstruction.

For purposes of illustration, a thyratron-type gaseousdischarge tube isillustrated in the drawing, as of the hydrogen-filled type, comprising asubstantially cylindrical ceramic envelope 1 containing a cup-shapedanode-electrode 3, having a substantially planar anode surface 3 andoutwardly extending heat-conducting and electrodeconnection flanges 3,solder-sealed at 2 between the upper edge of the ceramic envelope 1 andthe bottom edge of a cylindrical ceramic sealing ring 1 that assists inStates Patent O ICC ,2 Y giving mechanical strength Vto the seal. Theseal Zmay be of the `type described 'in the said vcopending applicationof vGoldberg and' Germeshausen. vCooperating withthe anode electrodesurface 3 is a closely-'spaced substantially parallel, preferably'apertured, planar lelectrode surface 5' of an inverted cup-shapedcontroler .grid electrode 5, also provided with outwardly extendingflanges "5,

similarly sealed at 2 between Vthe bottorn'edge of the fen-V in saidcopending application, in order to `provide longv arc-discharge paths.

vWithin the cup-'shaped control electrode :5 may -Vbe disposed a cathodeelectrode '7, illustrated 'as Ap'f an inverted cup-shape having similaroutwardly extending fanges 7 sealed at 2 between 'the ceramic ring 1"'and a ceramic base 9. y'l`l1ec'atlf-iode cup y7 may fcontain, at i-t'supper open end, a plurality of vane-type electrodes "f ofthe typedescribed in -a further copendingapplication, Serial No. 580,551,'ledApril25, 1956, by Ithe said applicants Germeshausen and 'Goldberg for,Electric-Discharge De-A vice and Cathode. A gas reservoir 11, ofthetype described, for example, lin application, 'Serial No. 714,086 filedFebruary 150,- 19513, by the said applicant Seymour Goldberg, et al.,for Gaseous Reservoir jand `Method,may be vdisposed within the cathodecup`7, `and may be heated by current 'passed along conductor-supports 11and 11". Above "the upper vsurface of the cathode vanes 7 may "dispose1a baille 13 having a central aperture 113. A :similar `.baille I5,having apertures 15" fsta'ggered so as 'to `be displaced from theapertures 4 of thesgrid-electrodefsurface 5 mayalsobeprovided. y. Inoperation, `dueto lthe presence of ionization in the. tube and theunavoidable existence of minutey :asymmetries, caused either -by -small-loose particles on the inner ceramic walllgordimens'ional inaccuracies,local regions :of the inner ceramic wall, such as 'the regioni betweentthe fdischa-rge region defined by vthe anode surface 3 yand the controlelectrode surface 5', may be bombarded to a greater extent with ions orelectrons (depending upon the asymmetries and the polarity of the anodepotential). These local regions will thus be caused because of theirnon-conductive properties, to charge to considerable voltages. Sincesuch local regions, charged to high voltage, are adjacent to otherregions of the ceramic wall 1 which are substantially uncharged, severeelectric-field gradients are set up. In tubes of this type, thepotential at the region P on the inside wall of the ceramic envelope 1,mid-way between the anode surface 3 Aand the control grid surface 5 maybe approximately l5 kilovolts. After the tube has been triggered, andinverse voltage is applied by oscillation in the circuit, or otherwise,between the anode 3 and control electrode 5, the potential at the regionP has not had time to decrease or bleed off. When the inverse voltage,which may be of the order of 10 kilovolts, becomes added to the 15-kilovolt potential upon the charged region P, a resultant potential of25 kilovolts may be produced. While the tube might hold off inversevoltages of the order of Vl0 kilovolts, the 25 kilovolts will causebreakdown in the in- Current will thus continue to flow withversedirection. out permitting the tube to recover before the next positivepulse is applied to trigger the same.

In accordance with the present invention, these prob- 3 inner wall 1 andthe side edges or walls of the electrodes 3 and 5. The band C ispreferably provided as a coating or layer upon the inner wall 1 itself,in the region P, and it has been found to have the effect of preventingthe above-mentioned accumulative charge upon the wallsV o'f the envelope1 in the region P. 'Such charge, to the contrary, will occur above theanode surface 3' or below the control electrode surface 5', but notopposite the Vdischarge region therebetween. To obtain best results, ithas been found that the band or conductive path C is preferably oflength at least equal to the length of the discharge region between theelectrode surfaces 3' and 5', but preferably extending somewhat beyond,both thereabove and thercbelow, along adjacent portions of lthe sidewalls of the cup-shaped electrodes 3 and 5, as shown.

This construction provides for a much higher breakdown voltage in theinverse direction. Considered from -a circuit viewpoint, the RC timeconstant inherent in the charged-wall region P of the ceramic envelope 1has been reduced by several orders of magnitude, permitting thepotential at the point P to decrease rapidly. Even if the region P isbombarded with an excess number of ions or electrons, intense localfields can not develop since the bombarding charges are readilyconducted away by the conducting path C. Instead, the potential of theentire conducting path C Will change, with no local intense fields inthe actual region near the anode surface 3.

. herent simplicity. Various predetermined potentials may Since theconductive path C has greater electrostatic capacity than a local regionof the ceramic Walls, variations in potential of the conductive path Cover a given time will be less than that which would occur at acorresponding region of the ceramic inner wall itself.

As an illustration, hydrogen thyratrons of this type have beenfabricated with two successive conductive-layer coatings C painted onthe region P and fired. The coating material was liquid-bright platinumconsisting of 50% platinum and 50% gold. The coating was in the form ofa band 3s-inch high on the inside surface, centered in the region Pbetween the anode surface 3' and the control electrode surface 5. Thetubes were tested in a pulse modulator circuit in which prior-artthyratrons, not incorporating the conductive path C, would hold offinverse voltages up to 14 kilovolts. The tube of the present inventionwith the conductive path C, on the other hand, was found to hold offinverse voltage spikes of at least also be applied to the conductivepath C, if desired.

Further modications will occur to those skilled in the art, and all suchare considered to fall within the spirit and the scope of the invention,as defined in the appended claims.

What is claimed is:

l. An electric-discharge device having, in combination, electrodesurfaces defining a discharge region therebetween and disposed within aninsulating envelope with the edges of the electrode surfaces spaced fromthe inner wall of the envelope, and a conductor electrically isolatedfrom the electrode surfaces and embracing the discharge region in thespace between said inner wall and said edges of the electrode surfaces,said conductor extending at least the length of the discharge regionbetween said electrode surfaces.

2. The discharge device of claim 1, said electrode surfaces includingcathode, anode, and grid electrode surfaces, said conductor surroundingsaid discharge region and extending at least `the length of thedischarge region between said anode and said grid electrode surfaces.

3. The discharge device of claim 1, one of said electrode surfaces beinga substantially planar surface of a rst cup-shaped electrode, the otherof said electrode surfaces being a substantially planar surface of asecond inverted cup-shaped electrode, said electrode surfaces beingsubstantially parallel.

4. The discharge device of claim 1, said conductor being mounted on theinner wall of said envelope.

References Cited in the le of this patent UNITED STATES PATENTS2,492,666 Sloan Dec. 27, 1949 2,654,850 Smith Oct. 6, 1953 2,739,262Watrous Mar. 20, 1956` 2,842,699 Germeshausen et al July 8, 1958

